1. Field of the Invention
The present invention relates to incremental position encoders and position interpolators and circuits for generating change of position signals with a high degree of accuracy. More particularly, the present invention relates to real time diagnostic and correction circuits for improving incremental encoder servo-signal performance at low and high speeds.
2. Description of the Prior Art
Rotary and linear encoders are well known to those skilled in the encoder art and it is also well known that when encoder sensors are moved relative to a rotary or linear scale, they may produce a square wave or sinusoidal analog output signal. These signals may be processed and counted to determine relative movement of the scale to the sensor head. When two sensor heads are employed in an incremental encoder system, one is phase-displaced 90 degrees from the other so that the simultaneous effective outputs may represent both magnitude and direction.
Encoder systems are employed to generate velocity signals by calculating the change of relative position as a function of time. The ability of a servo-positioner to perform its positioning function is dependent on the encoder system""s resolution accuracy and its ability to generate both position and velocity information.
Low velocity speeds generate signals which are unstable. This causes dithering and hunting in the servo-positioner being driven. It is also possible to incur spikes, blips and distortions at low critical speeds from noise coupling of the servomotor and other sources in the encoder system.
High or peak velocity speeds can produce loss of position due to illegal state changes as well from as the aforementioned spikes, blips and distortions.
Blips and distortions may also be caused by electronic noise, defective encoders and/or sensors as well as dirty or cracked or scratched encoder scales.
Heretofore, the manufacturers of encoders specified the preferred range of operable speeds to be used with their encoders. Customer/users are also aware that there is a range of acceptable speeds for encoders that should be even more restrained than the manufacturer""s recommendations.
Accordingly, it would be extremely desirable to provide an encoder system having an improved velocity profile for incremental encoders that automatically optimizes the performance and reduces error conditions.
It is a principal object of the present invention to provide an encoder system that reduces hunting at low speeds.
It is a principal object of the present invention to provide an encoder system with an improved output error signal.
It is a principal object of the present invention to provide an encoder system that smoothes out and/or eliminates noise spikes and blips permitting higher maximum velocities without sacrificing position accuracy.
It is a principal object of the present invention to detect an illegal state change in an encoder system which may have been caused by noise and/or defective encoder equipment.
It is a principal object of the present invention to provide a real time diagnostic evaluation of loss of position or state error in an incremental encoder system.
It is a principal object of the present invention to increase the speed of operation of incremental encoders by performing real time processing of input signal distortions and maintaining such distortions within predetermined tolerances.
It is yet another object of the present invention to analyze both state errors and input signal errors to determine if the errors are the result of excessive speed or noise or are due to faulty encoders.
It is yet another object of the present invention to provide a novel digital filter that substantially eliminates errors introduced by analog input signals.
It is a general object of the present invention to detect high velocity conditions which could create errors before they occur.
It is a general object of the present invention to employ digital filtered position vectors to optimize the minimum and maximum velocity in an incremental encoder system.
It is a general object of the present invention to match output signals to commercially available servo-controllers so that the servo-controller can handle the data rate of the information being supplied without errors.
It is a general object of the present invention to provide diagnostic logic means for determining the magnitude of noise and encoder induced errors to determine the source of the error.
It is a general object of the present invention to provide a high speed encoder system that is readily assembled from commercially available components such as complex programmable logic devices, digital signal processors and application specific programmable devices.
According to these and other objects of the present invention there is provided an incremental encoder system which comprises a pair of sensor/encoders arranged as a quadrature pair for producing analog position signals that are converted to digital signals which define a digital position vector and the presence or absence of an error. The digital position vector and the digital error signals are processed in a high speed logic device that is programmable to produce a filtered quadrature output capable of defining the position of the sensor relative to the encoder scale and its velocity. The system removes noise spikes and determines if there has been an illegal state change or state error.